The invention relates to optical signal transmission systems, and more particularly relates to optical signal band conversion apparatus.
The wavelengths of the optical signals transported over an optical fiber are typically within the so-called C-band, which ranges from 1530 nanometers (nm) to 1562 nm. The wavelengths of the optical signals in the C-band are derived using a semiconductor laser having a crystal and grating that are specifically designed to provide optical emission at those wavelengths. (As is well-known, the crystal provides the laser gain and the grating locks the laser to a specific frequency within the gain bandwidth.) Designers of optical equipment have greatly expanded the number of channels used in the C-band, and are now looking to use the so-called L-band (and other transmission bands, e.g., the so-called S-band) to further increase the number of useful channels that may be multiplexed onto a fiber path. The range of the L-band is from around 1562 nm to 1610 nm. Since the transmission equipment used to transmit optical signals over the C-band is specifically designed for the C-band, it cannot be used to transmit within the L-Band (or S-band). The reason for this is that the various equipments used to transmit optical signals are specifically engineered to operate in the C-band, as mentioned above for the C-band laser. That is, the performance of such equipment peaks in the C-band, but rolls off sharply in the L-band (and other transmission bands, e.g., the S-band). Consequently, one who desires to accurately transmit optical signals in other than the C-band needs to engineer the gain of the transmitter equipment, such as the laser crystal and grating as well as multiplexing equipment, specifically for the desired band, e.g., the L-band. Disadvantageously, it is difficult and expensive to engineer/design a crystal and grating for a laser as well as other transmission equipment to operate in a signal band other than the C-band.
We address the foregoing problems by employing equipment specifically designed for the C band and converting the C band signals to a second band, e.g., the L or S band, and then output the converted signals in place of the C-band signals. Specifically, in accordance with various aspects of the invention, a transmitter outputs optical signals having respective wavelengths within a first bandwidth, e.g., the C band. The latter signal is then combined with an optical signal having a wavelength between the first bandwidth and a second bandwidth, e.g., the L-band. A non-linear frequency converter processes the combined signal to form at least optical signals having wavelengths within the second bandwidth that correspond with the wavelengths of the optical signals within the first bandwidth. The converted signal is then supplied to respective output terminal, e.g., optical transmission path.
These and other aspects of the invention will be appreciated from the ensuing detailed description and accompanying drawings.